Gradient of the ZAPT2 energy

 An explicit expression for the analytical first derivative of the Z-averaged perturbation theory taken to second order energy, due to Lee and Jayatilaka, is presented for application to high-spin systems described by a restricted open-shell Hartree–Fock wavefunction. The use of frozen core orbitals is incorporated into the derivation. Received: 23 April 2001 / Accepted: 31 August 2001 / Published online: 9 January 2002     

Templating and selection in the formation of macrocycles containing [[P(micro-NtBu)(2)](micro-NH)](n) frameworks: observation of halide ion coordination

Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported.     

N2, C8-disubstituted guanosine derivatives can form G-quartets

A lipophilic guanosine with alkene groups attached to the nucleobase’s N2 and C8 positions was synthesized with the intent of using olefin cross-metathesis to covalently capture an individual G-quartet. Modification of the N2 and C8 positions gave a derivative that formed a stable G-quartet structure in the presence of a cation template. This is the first example of a N2, C8-disubstituted guanosine forming a G-quartet.     

Effect of excess sodium on the excitation of potassium in an air-acetylene flame: a steady state kinetic model which takes into account collisional excitation

Summary The effects of excess Na on the ionization and excitation of K in an air-acetylene flame were studied using absorbance signal and emission signal ratios, A/A and E/E respectively, as probes, where A and E are the line absorbance and line emission readings in the presence of excess Na interferent, and unprimed quantities represent readings in the absence of the interferent. An emission signal enhancement which increases exponentially as the ratio of interferent to analyte increases (up to about 2000), was observed irrespective of whether measurements were made from the primary or secondary reaction zones of the flame, while a similar line absorbance signal enhancement was observed only when measurements were made from the primary reaction zone. For both line emission and line absorbance, the maximum enhancements observed are in excess of those predicted on the basis of complete suppression of ionization of analyte atoms as a result of the increased partial pressure of electrons. A steady state kinetic model is presented, which takes into account radiative recombination collisional excitation of K⁺ ions and collisional charge transfer between the heavy particles, and whose predictions are consistent with the observed interference effects.     

Micellar electrokinetic chromatography of proteins

Micellar electrokinetic capillary chromatography (MECC) of proteins is a high resolution capillary electrophoretic (CE) analysis method that utilizes the hydrophobic and electrostatic interaction of protein analytes with surfactant micelles present in the buffer medium to facilitate separation. Through the manipulation of the protein-micelle interaction by the adjustment of variables such as surfactant concentration, solution pH, ionic strength, the presence of an organic modifier and the use of coated capillaries, MECC analyses of a wide variety of proteins have been optimized. MECC has been demonstrated to provide resolution of mixtures consisting of proteins with minor structural variations and also has provided the successful quantitative analysis of protein present in complex matrices. The adoption of protein MECC as a routine analytical technique may be dependent upon the successful interface of MECC with detection methodology, such as mass spectrometry, which can provide analyte characterization information.     

High temperature polymer blends: an overview of the literature

A review of work which has been performed on high temperature polymer blends is presented. The discussion is divided into miscible and immiscible blends. It is pointed out that one problem with miscible polymer blends is that of processing in the miscible state. In the case of immiscible blends, particularly ones containing liquid crystal polymers, the issue of adhesion of the two phases is discussed. Finally, the need for better theoretical models for predicting miscibility in polymer blends is highlighted.     

Comparison of silver results for canadian reference ores and concentrates and zinc-processing products by acid decomposition, tribenzylamine/chloroform extraction and fire-assay combined with atomic-absorption spectrophotometry

The results obtained for silver in Canadian reference ores and concentrates and in zinc-processing products by three atomic-absorption spectrophotometric methods are compared. "Wet chemical" methods based on the decomposition of the sample with mixed acids yield more accurate results than those based on fire-assay collection techniques. A direct acid-decomposition method involving the determination of silver in a 20% v/v hydrochloric acid-1% v/v diethylenetriamine medium is recommended for the determination of approximately 10 mug g or higher levels of silver. A method based on chloroform extraction of the tribenzylamine-silver bromide ion-association complex from 0.08M potassium bromide-2M sulphuric acid is recommended for samples containing < 10 mug of silver per g.     

Carbon dioxide emulsion assisted loading of polymer microspheres toward sustained release materials

An organic solvent-free method for encapsulating progesterone at high loadings within micron-sized inert latex polymer beads is reported. This approach makes use of a polymeric surfactant to emulsify carbon dioxide into an aqueous latex suspension. In this way, preformed approximately 4 microm polystyrene (PS) microparticles surface-grafted with poly(N-vinylpyrrolidone) (PVP) were plasticized and swollen followed by rapid partitioning of progesterone into the polymer matrix. The as-prepared polystyrene beads incorporated over 10% progesterone by weight while maintaining their initial size and morphological uniformity. Dissolution experiments were also carried out to obtain the release profile of progesterone entrapped within the PVP/PS particles.     

A hexa-peri-hexabenzocoronene cyclophane: an addition to the toolbox for molecular electronics

Cyclophanes with the largest-to-date polycyclic aromatic hydrocarbon (hexa-peri-hexabenzocoronene, HBC) to be entrained in such a structural motif are reported. The two disks are covalently captured by intermolecular ring-closing olefin metathesis of dienes in good yield. DSC, optical microscopy, and WAXD show the new cyclophanes to self-assemble to thermotropic columnar liquid crystal mesophases similar to monomeric analogues. Solution spectroscopic studies reveal that the two disks within a single unit lie face-to-face, with a small average lateral offset. Self-assembly into two-dimensional crystals at a solid-liquid interface was visualized by STM, and the electrical properties of single molecules were assessed by scanning tunneling spectroscopy revealing a diode-like behavior which is similar to that previously reported for single HBC disks, laying the groundwork for future electrical interrogations of dynamic molecular complexes.     

Tris(acetonitrile)tricarbonylchromium(0) catalyzed 1,4-addition of hydrogen to 1,3-dienes

The Cr(CO)₃(CH₃CN)₃ complex is found to catalyze the 1,4-addition of hydrogen to 1,3-dienes such as 2-methyl-1,3-butadiene, trans-1,3-pentadiene, and trans, trans-2,4-hexadiene at low temperature (40°) and low H₂ pressure (20 psi). For trans, trans-2,4-hexadiene the only product obtained when D₂ is used is 2,5-dideuterio-cis-3-hexene. The catalytic 1,4-hydrogenation can be carried out in neat dienes, and turnover numbers for the catalyst of greater than 3000 have been observed.